0 to 9 parts per million (ppm)
Normal - No Action: Typical from: outdoor sources, fumes from attached garages, heavy smoking, fireplace spillage and operation of unvented combustion appliances. With ambient conditions in this range, analysts may continue testing sequences.
10 to 35 parts per million (ppm)
Marginal: This level could become problematic in some situations. Actions: Occupants should be advised of a potential health hazard to small children, elderly people and persons suffering from respiratory or heart problems. If the home has an attached garage, document CO levels in garage. Accept this level as normal for unvented appliances but not for vented appliances. If unvented appliances are in operation, recommend additional ventilation in the areas of operation. With ambient conditions in this range, analysts may continue testing to locate the CO source.
36 to 99 parts per million (ppm)
Excessive: Medical Alert. Conditions must be mitigated. Actions: Ask occupants to step outside and query about health symptoms. Advise occupants to seek medical attention. If occupants exhibit any symptoms of CO poisoning, have someone drive them to a medical facility. Enter the building, open doors and windows to ventilate the structure. Turn off all combustion appliances until the CO level has been reduced to safe levels. If forced air equipment is available, continuos operation of the air handler is recommended at this time. If the home has an attached garage, document CO levels in garage. Test combustion appliances one at a time to determine the source of CO production. If an appliance is determined to be the source of CO production, it should be shut off and not used until a qualified technician with proper test equipment can service it.
100 - 200 parts per million (ppm)
Dangerous: Medical Alert. Emergency conditions exist. Actions: Evacuate the building immediately and check occupants for health symptoms. Advise all occupants to seek medical attention. Occupants should have someone else drive them to a medical facility. If occupants exhibit symptoms of CO poisoning, emergency service personnel must be called. Evacuation is important, but Analysts must not subject themselves to excessive conditions. Maximum exposure time is 15 minutes. Open all doors and windows that can be done quickly. If the home has an attached garage, document CO levels in garage. Disable combustion appliance operation. Continually monitor indoor ambient levels while moving through the building. Once the atmosphere within the structure has returned to safe levels and the appliances have been turned back on, locate the source of CO production for corrective measures.
Greater than 200 parts per million (ppm)
Dangerous: Medical Alert...
(source: Yahoo answers)
Health Effects of exposure to different values of carbon monoxide